A more robust and flexible lattice for LHC

To correct more efficiently the arc dispersion, the exact antisymmetry of the LHC optics is now broken, except in the low-/spl beta/ triplets common to the two rings. A new quadrupole is added between the experimental insertions and the dispersion suppressors and several are quadrupoles are complemented by a small trim quadrupole. The larger number of parameters gives flexibility to the lattice and allows a partial separation of the optical functions, with a decrease of the total number of quadrupole units. It is possible to change rather freely the phase advances of the are cells. The nominal tunes are split by 4 units to reduce coupling. The /spl beta/* tuning range in the experimental low-/spl beta/ is significantly increased, allowing e.g. a larger beam separation at injection. The super-periodicity of LHC remains 1. We plan to study whether it can be increased within the LHC hardware constraints.